The heat source of the high-speed electric spindle can be mainly divided into the following parts. First, the spindle motor is built in the structure of the machine tool spindle, and the heat generated by the high-speed rotation of the motor is the main heat source inside the structure. Second, the high-speed agitation of the rotor of the motor in the main shaft housing causes the air in the inner chamber to also generate heat. The heat generated by these heat sources is mainly dissipated through the main shaft housing and the main shaft, so that a considerable part of the heat generated by the electric motor passes through the main shaft. Going to the bearing, thus affecting the life of the bearing, and will cause the spindle to produce thermal elongation, affecting the machining accuracy. Third, as the spindle speed increases, the amount of heat generated by the friction of the spindle bearings also increases.
The heating of the motor mainly includes the copper loss heat of the stator winding and the iron loss heat of the rotor, wherein the heat of the stator winding accounts for more than 2/3 of the total heat generated by the motor. In the conventional cooling mode, only the stator portion is cooled, and the iron loss heat-generating portion of the rotor is not cooled, that is, the heat that accounts for nearly 1/3 of the total heat of the motor is not cooled, thereby forming The outside is cold inside. The thermal expansion of the rotor is fatal to the machining accuracy. If the spindle core is calculated according to the length of 500 mm, according to the metal expansion coefficient of the steel, the length of the spindle will be extended by 0.005 mm for each degree of temperature rise of the shaft core. In addition, for the cooling liquid that cools the bearing, under the centrifugal force of the high-speed rotating main shaft, the cooling liquid cannot be distributed to the inner ring and the shaft core of the bearing at all, and as the temperature rise of the main shaft increases, the pre-tightening amount of the bearing will increase. In turn, the heat of the bearing is exacerbated, so that the bearing is not effectively cooled and lubricated. Therefore, it is necessary to improve the cooling system of the conventional high-speed electric spindle.
2. Working principle and characteristics analysis of heat pipe
The heat pipe is one of the most efficient heat transfer components known to mankind. The heat pipe is sealed in the high vacuum cavity by means of a phase change of the working medium. The work is continuous and can pass a large amount of heat. The small cross-sectional area is transmitted over long distances and no external power is required. Since there are no failed operating parts, the heat pipe operation is very reliable. The working principle of the heat pipe is shown in Figure 2. The liquid working medium is heated in the evaporation section and is evaporated. In the vacuum chamber, the vaporized vapor flows rapidly through the adiabatic section to the condensation section, and the heat in the evaporation section is also carried to the condensation section. In the condensation section, the steam hits the cooling fluid outside the tube and exchanges heat and cold to release heat from the evaporation section. As the steam loses thermal energy, it forms a condensate in the wick of the condensation section. The condensate returns to the evaporation section and then absorbs heat and evaporates under the action of the capillary wicking force. In the three working sections of the heat pipe, the evaporation section and the condensation section are indispensable, and the adiabatic section is optional according to the design requirements. In the actual heat pipe structure, there is usually no adiabatic section.
Figure 2 Heat pipe working principle diagram
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